1. Field of the Invention
This invention relates a process for manufacturing a sole, more particularly to a process for manufacturing an ethylene vinyl acetate sole.
2. Description of the Related Art
Conventionally, EVA (ethylene vinyl acetate) soles are formed by the following steps:
(1) weighing manually the molding compounds for manufacturing the EVA sole;
(2) mixing the molding compounds in a dispersion kneader;
(3) blending and calendering the molding compounds in a roll-mixer;
(4) extruding the molding compounds by means of a single screw extruder so as to form spaghettilike extruded outputs, the weight of each of the extruded outputs being controlled by a gear pump;
(5) placing the extruded outputs in a heated, pressurized first mold so as to form a rough foamed sole;
(6) trimming the rough foamed sole;
(7) placing the rough foamed sole in a heated, pressurized second mold so as to form a finished EVA sole.
The conventional process for manufacturing the EVA sole suffers from the following disadvantages:
(1) The process is quite complicated and is time-consuming and labor-intensive.
(2) Bulky mixing, blending and calendering apparatuses are used in the conventional process, occupying a lot of working space.
(3) The rotating speed of the screw of the single screw extruder must be controlled (i.e., cannot be too fast) in order to prevent excessive heat, which results from the friction between the molding compounds and the screw shaft of the single screw extruder and causes the EVA to foam prematurely. The too early foamed EVA causes the extruded outputs to be unsuitable for further processing. In addition, the single screw extruder will be damaged by the excess heat. Therefore, the production rate of the EVA sole cannot be high.
(4) The defect ratio of the spaghettilike extruded outputs is high.